Method and apparatus for pumping liquid metal alloys

ABSTRACT

This invention provides an improved method and apparatus for controlling the flow of molten metal alloys and, in particular, to a method to finely control the delivery rate of liquid aluminum alloys and the liquid fraction of semi-solid aluminum alloys. The apparatus and method described herein provide for the pumping of liquid metal alloys in a precise and controlled manner. By controlling the heat flow through a section of the pump piston, the pump chamber, the porous liner of the pump chamber and the metal alloy charge, the present invention provides a means to deliver liquid metal alloys at high pressure through one or more exit ports.

FIELD OF THE INVENTION

The present invention is directed to an improved method and apparatus for the controlling the flow of liquid metal such as metal alloys and separating the liquid and solid fractions of semi-solid alloys. The .apparatus and method described herein provide for the pumping of liquid metal alloys in a precise and controlled manner. By controlling the heat flow through a section of the pump piston, the pump chamber, the porous pump chamber liner and the metal alloy charge, the present invention provides a means to deliver liquid metal alloys at high pressure through one or more exit ports.

BACKGROUND OF THE INVENTION

In modern industrial practice, the transfer of molten metal, particularly aluminum alloys, for purification or casting can be difficult to control in a repeatable manner. Given the high temperatures required to bring most metals to a liquid state, and frequently, the chemical reactivity of liquid metals with their containment vessels and the atmosphere, the process of pumping metal from the melt crucible to the desired location is technologically challenging. For liquid aluminum alloys, a family of liquid metal pumps has been created (U.S. Pat. Nos. 5,947,705, 5,785,494, 6,551,060) to pressurize the liquid metal to assist in the transfer of the metal from the crucible to the desired location. The pressure afforded by such pumps (often measured using the concept of metallostatic head—the pressure required to pump a given liquid metal to given height against gravity) tends to be low, generally less than one atmosphere of pressure (a metallostatic head of 760 mm for the liquid metal mercury). Because of these low pressures, the height to which liquid metal can be delivered and the force with which the metal can be transferred by such pumps is limited. Additionally, the volumetric flow rates afforded by such pumps must typically be quite high, if only to prevent the premature freezing (solidification) of the liquid metal alloy prior to delivery. In consequence of these limitations, conventional liquid metal pumps are not useful in applications where the metal delivery rate is required to be tightly controlled, such as the delivery to an exit port where the melt is to be cast into fine shapes.

One method to deliver liquid aluminum alloys at higher pressures for the casting of fine, thin walled shapes is through the process known as die casting (U.S. Pat. Nos. 10,894,286, 10,821,504, 9,889,500). In this method, the melt is poured (generally by gravity feed from a melting crucible) into the breach of the die casting cylinder. On the closing of the breach, a piston rapidly compresses the melt, forcing the liquid to pass through a small orifice at many meters per second to create a spray of fine metallic droplets that coat the inside of a steel die. Generally a second even higher pressure is imposed following the initial metal delivery in an effort to close any porosity remnant in the die casting prior to solidification. Such die castings, however, still tend to suffer from some level of remnant porosity and cannot generally be used in fluid-tight applications, such as brake cylinders in vehicles or fuel rails in internal combustion engines. Other piston-driven liquid metal pump systems, such as those employed in semi-solid casting (U.S. Pat. Nos. 5,879,478, 5,571,346, 7,323,069) suffer similar technical shortfalls, including melt separation, non-homogeneous composition, and the high equipment costs associated with the tight machining tolerances required to maintain metallostatic pressure at high temperatures.

An additional problem associated with the casting of aluminum alloys is the degradation in metallurgical purity associated with the recycling. For economic reasons, the majority of industrial aluminum alloy castings are produced using recycled aluminum. Unfortunately, there is generally very little (if any) segregation of the scrap used in the formulation of the casting stock. As a result, the elemental additions used in the formulation of different aluminum alloys (such as silicon, magnesium, manganese and others) tend to accumulate in castings made with high recycle content, often leading to a degradation in the performance of the casting itself. A means to segregate or purify the charge prior to casting the alloy into product is therefore advantageous.

It is therefore desirable to produce a method and an apparatus that provides for the controlled delivery of liquid metal alloys at variable pressures and volumetric flow rates as well as a means of purifying the composition of the alloy. The operation of an invention to provide finely controlled delivery and refinement of liquid or semi-solid metal alloys is described here. The invention provides a flow of liquid metal to a single exit port or group of exit ports in fluid connection with the alloy melt charge in a manner that allows for fine control of the imposed pressure and the flow of liquid metal alloys through these ports. Additionally, the invention provides for a means to segregate the liquid component of a melt charge from the solid component of a melt charge and thereby refine the alloy composition. The apparatus described provides for means to create a pressure seal above a liquid or semi-solid charge to permit the pressurization of the charge and promote flow while avoiding the deleterious effects of chemical attack on pump components by control of the thermal flux between the melt charge, the pump chamber and the pump piston.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the present invention to provide an apparatus and method to provide a semi-continuous flow of liquid metal alloys in a controlled manner through a piston pump.

Another object of the present invention is a method of providing a pressure seal between the liquid or semi-solid metal alloy charge and the surrounding atmosphere.

Another object of the present invention is a method of maintaining a pressure seal between the liquid metal alloy charge and the surrounding atmosphere by controlling the temperature of the metal alloy charge residing in the annulus between the side walls of the piston bearing and the inner walls of the piston chamber. The solidity of this annulus and the integrity of the pressure seal are controlled by the temperature of the annulus. By maintaining a positive heat flux radially inward, from the piston chamber toward the cooled outer wall of the piston bearing, a layer of high viscosity solid or semi-solid metal is formed to provide a pressure tight seal, allowing for high pressure to be imposed upon the metal alloy charge. The axial motion of the pump piston within the piston chamber, therefore, is both lubricated and sealed by the high viscosity solid or semi-solid annulus of the alloy charge between the piston wall and the piston chamber. As the temperature of this solid or semi-solid layer is controlled by the heat flux between the piston chamber walls and the walls of the piston, tight machining clearance between the piston and the cylinder are not required, greatly reducing the cost of manufacturing of the pump itself. As the inner surface of the annulus in contact with the actively cooled section of the piston wall will be solidified, the chemical reactivity between the piston material and the melt charge is greatly reduced. Maintaining this solid annulus of alloy around this section of the piston provides the pressure seal and eliminates the problem of wear and physical erosion generally associated with the pressure bearing seals on piston pumps. Controlling the velocity of the piston provides for control over the metal flow rate down to a flow rate of zero. The force on the piston provides a measure of the metallostatic pressure.

One other object of the present invention is an apparatus for pressurizing a liquid or semi-solid metal alloy charge wherein the working surfaces of the pump in contact with the charge (defined here as the piston chamber walls, the piston face, and the exit port at the opposite end of the chamber from the piston face) are at or near the temperature of the metal alloy charge to be pumped. As these working surfaces are maintained in a compressional state of stress and do not require tight machining tolerances to maintain the pressure seal, they may be constructed of easily machined, low cost materials.

One other object of the present invention is an apparatus utilizing the pressurization of a semi-solid metal alloy charge to separate the liquid fraction and the solid fraction of this charge through a porous lining of the pump chamber. By maintaining the temperature of the metal alloy charge to be pumped at a temperature between the solidus and the liquidus of the charge, the liquid fraction of the charge may be forced through the porous liner to the exit port under action of the imposed pressure. As the composition of the charge within the chamber liner will change as the liquid fraction of the charge is removed (the composition of the liquid and solid fractions of an alloy in a semi-solid state being preferentially enriched or depleted of elemental alloying additions), the charge can thus be purified and lower melting components of the charge removed. Increasing the temperature of the charge allows for further separation and removal of multiple low melting components of the semi-solid charge, thus further refining the composition of the charge itself.

Other objects and advantages of the present invention will become apparent as a description thereof proceeds.

In satisfaction of the foregoing objects and advantages, the present invention comprises an improvement in the transfer of metal alloy. A method of operation to supply metal alloy to a downstream operation is to charge the piston chamber with metal alloy by withdrawal of the pump piston and filling the chamber with an metal alloy. The metal alloy charge may be in a liquid state and transferred from a melting crucible or may be in solid state and transferred from a hopper. The alloy charge may then be heated by a heating jacket that surrounds the piston chamber. Induction heating, resistance heating or flame impingement are examples of three such heating jackets. The charge, when heated to a temperature above the solidus of the metal alloy, may now be compacted by the axial motion of the piston within the piston chamber. Air or other gasses, remnant from the charging process, will now be forced out of the cylindrical piston chamber through the gap between chamber walls and the piston walls. If the port on the opposite end of the cylinder from the piston remains closed, the axial motion of the piston will now drive the liquid or semi-solid charge into the annulus between piston outer wall and the inner wall of the chamber.

The apparatus may also include a cooling channel within the piston to provide cooling using either air, water or a combination of both. By controlling the flow of air and/or water through this channel, the liquid charge can be made to freeze on the outer surface of the piston section, creating a solid annulus of metal alloy around this section of the piston. As the cooled section of the piston can be thermally separated from the working surface of the piston (i.e. the face of the piston), a pressure seal composed of the solidified melt charge can be maintained around this section during axial motion of the piston, allowing for a high metallostatic pressure to be imposed upon the metal alloy charge.

The apparatus may also include a porous liner within the piston chamber to provide a fluid path for the removal of the liquid fraction of the charge. By controlling the temperature of the charge, the liquid fraction can be forced through the chamber lining and directed toward the exit port. Through control of the charge temperature, the lower melting components of the charge can thereby be removed and the charge composition purified.

In one embodiment of the invention, a single piston may be used within the piston chamber. In this embodiment, an exit port is provided at the opposite end of the piston chamber from the piston face. The flow of melted charge through this exit port is controlled by the opening and closing of a fluid passage through the body of the exit port. In this embodiment, the opening and closing of this passage is controlled by the application of heat to the body of the exit port, allowing the free flow of the liquid fraction of the charge when the temperature of the exit port is brought above the liquidus of the alloy. The exit port, in this embodiment, therefore functions as a valve, wherein the charge is in fluid contact with the full length of the passage when the body of the exit port is above the liquidus of the charge. When the body of the exit port is below the solidus of the melt charge, this passage will be occluded by the solidification of the charge, effectively closing the valve. In this embodiment, the passage through the exit port can be used to meter small droplets of the melt charge for the deposition of fine metal droplets onto a workpiece or substrate. In this embodiment the semi-continuous flow of liquid metal alloy can be used in 3D metal printing, high pressure die casting and metal powder production.

In another embodiment of this invention, a porous chamber liner is positioned within the piston chamber and in physical and thermal contact with the piston chamber. In this embodiment, the liquid fraction of the charge is forced through the porous liner to the exit port under the action of the piston. The liquid fraction is then drained from the melt, leaving the solid fraction of the charge within the chamber liner. Increasing the temperature of the charge through the use of the chamber heat jackets promotes additional melting, allowing for this higher melting temperature liquid fraction to be drained from the charge. As the charge can be progressively heated and pressurized, this embodiment permits the selective partitioning of the low melting components of the charge and controlled flow of these low melting components sequentially through the exit port. In this embodiment the semi-continuous flow of liquid metal alloy can be used in melt separation, melt purification and recycling.

In another embodiment of this invention, an exit port is provided near the center of the piston chamber between two movable pistons. Here the pistons may be operated singularly or in tandem to pressurize the charge and the liquid in the charge is forced through the exit port between the two pistons. The flow of melt charge through this exit port is controlled by the opening and closing of a fluid passage through the body of the exit port. In this embodiment, the opening and closing of this passage is controlled by the application of heat to the body of the exit port, allowing the free flow of the liquid fraction of the charge when the temperature of the exit port is brought above the solidus of the melt charge. The exit port, in this embodiment, therefore functions as a valve, wherein the charge is in fluid contact with the full length of the passage when the body of the exit port is above the solidus of the charge. When the body of the exit port is below the solidus of the charge, this passage will be occluded by the solidification of the charge, effectively closing the valve. By supplying metal alloy charge to inlet ports within the stroke of the two pistons, the semi-continuous flow can now be made fully continuous.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic of the first embodiment of the invention employing a employing a single piston and a single pressure seal; and

FIG. 2 is a schematic of the second embodiment of the invention employing a single piston, a single pressure seal and a porous chamber liner; and

FIG. 3 is a schematic of the third embodiment of the invention employing dual opposing pistons and two pressure seals.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a means of sealing the pressure within a piston chamber to deliver liquid metal alloys at high pressure through one or more exit ports or outlets. The present invention also provides for an apparatus for applying pressure to control the flow of such aluminum alloys through the controlled motion of one or more pistons, and for the use of this pressure to separate the liquid fraction of a charge from the solid fraction. The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accompanying drawings, like and/or corresponding elements are referred to by like reference characters.

Referring to FIG. 1, the first embodiment employing a single piston pump is described. The pump apparatus is comprised of a movable pump piston assembly 1 within a piston chamber 2 with an exit port assembly 3 affixed at the opposing end of the piston chamber from the piston. The piston assembly 1 is comprised of a piston face 1 a which is mechanically linked and in physical and thermal contact with the piston bearing 1 b. The piston bearing 1 b is sized so as to provide a loose fit within the walls 2 a of the piston chamber so as to allow for free translational motion of piston within the piston chamber walls. The piston bearing is affixed to a hollow cooling shaft 1 c. Intermediate thermal insulation rings 1 d may be positioned between the cooling shaft and the piston bearing to modulate heat flow from the piston bearing to the cooling shaft. The cooling shaft 1 c is comprised of a co-axial cooling chamber 1 e wherein coolant 4 (water, air or a water/air mixture) is pumped through the central conduit 1 f and returned via the annular conduit 1 g so as to provide active cooling to the piston bearing.

In further reference to FIG. 1, the piston chamber 2 is comprised of the piston chamber walls 2 a, the piston chamber pressure vessel 2 b enclosing and in mechanical contact with the piston chamber walls, and heating jackets 2 c. The heating jackets may be comprised of induction heaters, resistance heaters or gas heaters. Enclosing the heating jackets 2 c is thermal insulation 2 d.

In yet further reference to FIG. 1, the pump apparatus comprises an exit port body 3 positioned at the opposing end of the piston chamber 2 from the movable piston assembly 1. The port body is comprised of a central fluid passage 3 a to provide egress of the liquid portion of the metal alloy charge. The port body may be heated by port body heaters 3 b to control the temperature of the port body so as to promote the melting or freezing of the metal charge within the central fluid passage. Removable filter materials 3 c, commonly used in the processing of liquid aluminum alloys, may be inserted between the piston chamber walls 2 a and the exit port 3.

In yet further reference to FIG. 1, the operation of the apparatus is as follows:

-   -   the piston assembly 1 is withdrawn from the piston chamber 2;     -   an metal alloy charge 5 is loaded into the piston chamber. This         charge may be in solid form (as chips or turnings) or in liquid         form;     -   the piston assembly 1 is then re-inserted into the heated piston         chamber 2 and the charge compacted;     -   the exit port body 3 is maintained at a temperature below the         solidus of the charge 5 so as to occlude the fluid passage and         prevent premature leaking of the liquid charge;     -   upon compaction of the liquid or semi-solid charge, liquid metal         alloy will be forced into the annulus 5 a between the piston         chamber lining 2 a and the lands of the piston bearing 1 b, the         lands of the piston bearing 1 b so configured as to provide a         series of two or more grooves 1 h wetted by the liquid metal,         which, upon solidification in contact with cooled piston bearing         act to provide a pressure tight seal between the piston bearing         and the piston chamber lining.

In final reference to FIG. 1, the piston assembly 1 is translated into the piston chamber 2 forcing liquid metal alloy charge 5 through the heated exit port 3 to provide a controlled flow of charge through the fluid passage under controlled pressure. The process above is then repeated upon re-charging of the pump apparatus to provide semi-continuous flow.

Referring to FIG. 2, the second embodiment employing a single piston and a porous piston chamber lining is described. The pump apparatus is comprised of a movable pump piston assembly 1 within a piston chamber lining 7, within a piston chamber 2 with an exit port assembly 3 affixed at the opposing end of the piston chamber from the piston. The piston assembly 1 is comprised of a piston face 1 a which is mechanically linked and in physical and thermal contact with the piston bearing 1 b. The piston bearing 1 b is sized so as to provide a loose fit within the lining of the piston chamber 7 so as to allow for free translational motion of piston within the piston chamber lining. The piston bearing is affixed to a hollow cooling shaft 1 c. Intermediate thermal insulation rings 1 d may be positioned between the cooling shaft and the piston bearing to modulate heat flow from the piston bearing to the cooling shaft. The cooling shaft 1 c is comprised of a co-axial cooling chamber 1 e wherein coolant 4 (water, air or a water/air mixture) is pumped through the central conduit 1 f and returned via the annular conduit 1 g so as to provide active cooling to the piston bearing.

In further reference to FIG. 2, the porous piston chamber liner 7 is installed within chamber 2 in thermal and mechanical contact with the piston chamber walls 2 a, with the piston chamber walls in mechanical contact with the pressure vessel 2 b. The heating jackets 2 c surround the pressure vessel. The heating jackets may be comprised of induction heaters, resistance heaters or gas heaters. Enclosing the heating jackets 2 c is thermal insulation 2 d.

In yet further reference to FIG. 2, the pump apparatus comprises an exit port body 3 positioned at the opposing end of the piston chamber from the movable piston assembly. The port body is comprised of a central fluid passage 3 a to provide egress of the liquid fraction of the metal alloy charge. The port body may be heated by port body heaters 3 b to control the temperature of the port body so as to promote the melting or freezing of the metal charge within the central fluid passage. Removable filter materials 3 c, commonly used in the processing of liquid aluminum alloys, may be inserted between the piston chamber walls 2 a and the exit port 3.

In yet further reference to FIG. 2, the operation of the apparatus is as follows:

-   -   the piston assembly 1 is withdrawn from the piston chamber 2;     -   an metal alloy charge 5 is loaded into the piston chamber. This         charge may be in solid form (as chips or turnings) or in liquid         form;     -   the piston assembly 1 is then re-inserted into the heated piston         chamber 2 and the charge compacted;     -   the exit port body 3 is maintained at a temperature below the         solidus of the charge 5 so as to occlude the fluid passage and         prevent premature leaking of the liquid charge;     -   upon compaction of the liquid or semi-solid charge, liquid metal         alloy will be forced into the annulus 5 a between the piston         chamber lining 2 a and the lands of the piston bearing 1 b, the         lands of the piston bearing 1 b so configured as to provide a         series of two or more grooves 1 h wetted by the liquid metal,         which, upon solidification in contact with cooled piston bearing         act to provide a pressure tight seal between the piston bearing         and the porous piston chamber lining 7.

In final reference to FIG. 2, the piston assembly 1 is translated into the piston chamber 2 forcing the liquid portion of the metal alloy charge 5 through the porous liner 7 and into the heated exit port 3 to provide a controlled flow of the liquid fraction of the charge through the fluid passage. With the liquid fraction of the charge now being ejected from the exit port, the solid fraction of the charge can be further heated, permitting the subsequent liquid fractions of the (now hotter) charge to be forced through the porous liner and the exit port. The process above is then repeated upon re-charging of the pump apparatus to provide semi-continuous flow.

Referring to FIG. 3, the third embodiment employing a dual piston pump is described. The pump apparatus is comprised of two movable pump pistons, pump assembly 1 and pump assembly 6, within a piston chamber 2 with an exit port assembly 3 positioned in the piston chamber between the piston faces 1 a and 6 a. The piston assembly 1 is comprised of a piston face 1 a which is mechanically linked and in physical and thermal contact with the piston bearing 1 b. The piston bearing 1 b is sized so as to provide a loose fit within the walls 2 a of the piston chamber so as to allow for free translational motion of piston within the piston chamber lining. The piston bearing is affixed to a hollow cooling shaft 1 c. Intermediate thermal insulation rings 1 d may be positioned between the cooling shaft and the piston bearing to modulate heat flow from the piston bearing to the cooling shaft. The cooling shaft 1 c is comprised of a co-axial cooling chamber 1 e wherein coolant 4 (water, air or a water/air mixture) is pumped through the central conduit 1 f and returned via the annular conduit 1 g so as to provide active cooling to the piston bearing.

The piston assembly 6 is comprised of a piston face 6 a which is mechanically linked and in physical and thermal contact with the piston bearing 6 b. The piston bearing 6 b is sized so as to provide a loose fit within the walls 2 a of the piston chamber so as to allow for free translational motion of the piston within the piston chamber lining. The piston bearing is affixed to a hollow cooling shaft 6 c. Intermediate thermal insulation disks 6 d may be positioned between the cooling shaft and the piston bearing to modulate heat flow. The cooling shaft 6 c is comprised of a co-axial cooling chamber 1 e wherein coolant 4 (water, air or a water/air mixture) is pumped through the central conduit 6 f and returned via the annular conduit 6 g so as to provide active cooling to the piston bearing.

In further reference to FIG. 3, the piston chamber 2 is comprised of the piston chamber walls 2 a, the piston chamber pressure vessel 2 b and heating jackets 2 c. The heating jackets may be comprised of induction heaters, resistance heaters or gas heaters. Enclosing the heating jackets 2 c is thermal insulation 2 d.

In yet further reference to FIG. 3, the pump apparatus comprises an exit port body 3 positioned between the opposing pistons in the piston chamber. The port body is comprised of a central fluid passage 3 a to provide egress of the liquid or semi-solid metal alloy charge. The port body may be heated by port body heaters 3 b to control the temperature of the port body so as to promote the melting or freezing of the metal charge within the central fluid passage. Removable filter materials 3 c, commonly used in the processing of liquid metal alloys, may be inserted between the piston chamber lining 2 a and the exit port 3.

In yet further reference to FIG. 3, the operation of the apparatus is as follows:

-   -   the piston assembly 1 or 6 is withdrawn from the piston chamber         2 and;     -   an metal alloy charge 5 is loaded into the piston chamber. This         charge may be in solid form (as chips or turnings) or in liquid         form;     -   the piston assembly 1 or 6 is then re-inserted into the heated         piston chamber 2 and the charge compacted;     -   the exit port body 3 is maintained at a temperature below the         solidus of the charge 5 so as to occlude the fluid passage and         prevent premature leaking of the liquid charge;     -   upon compaction of the liquid or semi-solid charge, liquid metal         alloy will be forced into the annulus 5 a between the piston         chamber lining 2 a and the lands of the piston bearing 1 b, the         lands of the piston bearing 1 b so configured as to provide a         series of two or more grooves 1 h wetted by the liquid metal,         which, upon solidification in contact with cooled piston         bearing, key into the piston bearing in intimate physical and         thermal contact so as to create a pressure tight seal between         the piston bearing and the piston chamber walls. Liquid metal         alloy will also be forced into the annulus 5 b between the         piston chamber walls 2 a and the lands of the piston bearing 6         b, the lands of the piston bearing 6 b so configured as to         provide a series of two or more grooves 6 h wetted by the liquid         metal, which, upon solidification in contact with cooled piston         bearing, key into the piston bearing in intimate physical and         thermal contact so as to create a pressure tight seal between         the piston bearing and the piston chamber walls.

In final reference to FIG. 3, piston assembly 1 or piston assembly 6 is extended into the piston chamber 2 forcing liquid metal alloy charge 5 through the heated exit port 3 to provide a controlled flow of charge through the fluid passage under controlled pressure. The process above is then repeated upon re-charging of the pump apparatus to provide semi-continuous flow.

As such, an invention has been disclosed in terms of preferred embodiments thereof which fulfills each and every one of the objects of the present invention as set forth above and provides a new and improved method and apparatus to deliver liquid metal alloys in finely controlled measured amounts through one or more ports.

Of course, various changes, modifications and alterations from the teachings of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof. It is intended that the present invention only be limited by the terms of the appended claims.

It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Such modifications are to be considered as included within the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. 

What is claimed is:
 1. A method to deliver a liquid metal alloy charge in controlled amounts through one or more ports by creating a pressure tight seal between the walls of a piston chamber and a movable piston, the pressure tight seal being composed of a solid annulus of the metal alloy charge.
 2. The method of claim 1 wherein the solid annulus is maintained using a cooling channel in thermal contact with a section of the movable piston.
 3. The method of claim 1 wherein the movable piston is used to pressurize the liquid or semi-solid metal alloy charge to facilitate the delivery of the charge to a port or a group of ports.
 4. An apparatus to deliver a liquid metal alloy charge in controlled amounts through one or more ports by creating a pressure tight seal between the walls of a piston chamber and a movable piston, the pressure tight seal being composed of a solid annulus of the metal alloy charge.
 5. The apparatus of claim 4 wherein the solid annulus is maintained by a cooling channel in thermal contact with a section of the movable piston.
 6. The apparatus of claim 4 wherein the movable piston is used to pressurize the liquid or semi-solid metal alloy charge to facilitate the delivery of the charge to a port or a group of ports.
 7. A method to deliver a liquid fraction of an metal alloy charge in controlled amounts through one or more ports by creating a pressure tight seal between the porous liner of a piston chamber and a movable piston, the pressure tight seal being composed of a solid annulus of the metal alloy charge.
 8. The method of claim 7 wherein the solid annulus is maintained by a cooling channel in thermal contact with a section of the movable piston.
 9. The method of claim 7 wherein the movable piston is used to pressurize the liquid or semi-solid metal alloy charge to facilitate the delivery of the liquid fraction of a charge to a port or a group of ports.
 10. An apparatus to deliver a liquid fraction of an metal alloy charge in controlled amounts through one or more ports by creating a pressure tight seal between the porous liner of a piston chamber and a movable piston, the pressure tight seal composed of a solid annulus of the metal alloy charge.
 11. The apparatus of claim 10 wherein the solid annulus is maintained by a cooling channel in thermal contact with a section of the movable piston.
 12. The apparatus of claim 10 wherein the movable piston is used to pressurize the liquid or semi-solid metal alloy charge to facilitate the delivery of the liquid fraction of a charge to a port or a group of ports. 